In HPLC, high-pressure switching valves are used for a wide variety of different tasks, for example for extracting a sample to be examined from a sample vessel, feeding said sample into a sample loop and introducing the sample from there into a high-pressure liquid stream in the direction of a chromatography column, or for flushing various components or for switching between multiple columns.
Such switching valves are generally installed in automatic sample input devices for HPLC, in column ovens or in fraction collectors.
When using switching valves, it is almost always advantageous for the medium to be controlled to flow through only short capillary paths between the respective components. For example, in the case of samples being conducted in an eluent flow, it is advantageous for only short capillary paths to have to be covered, because then the dispersion of the sample, that is to say the mixing of the sample with the eluent situated in the fluid path upstream and downstream of the sample, is low. Furthermore, as a result of the short capillary paths, the pressure loss in the respective system is minimized.
To attain short capillary paths, it is advantageous, or in many cases imperative, for the switching valve to be of the most compact construction possible. In this way, the switching valve can be used in a space-saving and variable manner.
Despite a compact construction, a switching valve of said type must self-evidently also ensure precise and reproducible positioning of the moving parts which guide the medium to be controlled.
Switching valves such as are used for introducing a sample into the fluid stream normally have a stator in which there are provided multiple connection ports for the supply and discharge of the fluid to and from the switching valve. The ports are connected via ducts to opening cross sections which are formed on a switching surface of the stator, for example on the face side of a substantially cylindrical stator element. The rotor likewise has a switching surface which interacts with the switching surface of the stator, wherein in the switching surface of the rotor there are formed grooves which serve to connect certain opening cross sections and/or ports of the stator to one another as a function of two or more switching positions. Here, the rotor and the stator must be pressed against one another with an adequately high pressing force in order to attain a sealing action in the plane of the switching surfaces even in the case of high pressures such as arise in liquid chromatography, in particular HPLC.
Such switching valves are described for example in WO 2009/101695 A1 or in US 2010/0281959 A1.